The present invention relates to an automatic power-driven screwdriver for tightening screws in a horizontal direction, and more particularly to an automatic screw tightening machine having a chute for feeding screws with their shanks hanging down and an index mechanism for orienting the screws in a horizontal direction before they are advanced and tightened by a screwdriver bit.
Various automatic screwdrivers have been used for tightening screws one by one in a horizontal direction. One form of such horizontal screw tightening machine comprises a chute for supplying screws arranged in a row, a tube for feeding the screws under pneumatic pressure one by one from the chute into a Y-shaped pipe, a pair of pivoted jaws mounted on the Y-shaped pipe for gripping one of the screws at a time, and a screwdriver bit reciprocably mounted in the Y-shaped pipe for driving the screw into a workpiece after the Y-shaped pipe has been advanced toward the workpiece. The tube for pneumatically forcing the screws into the Y-shaped pipe has a bore which is only slightly larger in diameter than the heads of the screws to be fed therethrough so that the screws can effectively be propelled without substantial air leakage past the screw heads. Therefore, the known screw tightening machine lacks versatility as it cannot tighten those screws which have head diameters that do not fit the tube bore.
Another prior horizontal screwdriver includes a chute on which screws are vertically supported in a horizontal row. A suction pipe draws screws one by one from the chute under a vacuum into the suction pipe, and a screwdriver bit concentrically disposed in the suction pipe for tightening the screws. The suction tube and screwdriver bit are reciprocably movable between a vertical position in which a screw is introduced into the suction tube and a horizontal position in which the screw is driven by the screwdriver bit out of the suction pipe into a workpiece. The screw tightening machine, with a mechanism required for moving the suction tube and screwdriver bit, is relatively large in size and complicated in structure, and one cycle of operation of the machine requires a relatively long period of time for each screw to be applied.